1. Field of the Invention
The present invention relates generally to an aluminum type alloy having high seizure resistance, fatigue-resistance and so forth and having light weight. More specifically, the invention relates to an aluminum type alloy suitable for use as bearing metal for producing bearings, sliding member and so forth for automotive vehicles, industrial machines, agricultural machines and so forth.
2. Description of the Background Art
Various bearing metals, such as Cu-Pb type metal alloy, babbitt metal and so forth are selectively used as material for producing slide bearing depending upon use of the bearing. In the automotive industries, attention has been attracted to an aluminum type alloy for a bearing metal for bearings employed in an internal combustion engine, for its high heat-resistance, wear-resistance, corrosion-resistance, fatigue-resistance and so forth. Particularly, Al-Sn type alloys, Al-Sn-Pb type alloys have been considered to have better or more suitable property for use in automotive internal combustion engine.
On the other hand, in the recent days, the automotive internal combustion engines have been required smaller size and lighter weight. To answer such requirement, components of the engine have become smaller. Naturally, an axial length of the bearings are reduced. In contrast to this, the modern type engine have been grown to produce higher power for higher performance. This subjects the bearings in the engine much severe condition. Such severe condition of use of the bearing encounters various problems. Namely, under severe condition of use in the modern and high performance engine, formation of crack, local spolling from backing steel becomes serious problems. Therefore, providing sufficiently high fatigue-resistance becomes important task.
In order to answer this, the owners of the present invention has proposed new type bearing metal in Japanese Patent First (unexamined) Publication (Tokkai) Showa 62-130253. The proposed material is generally composed of Al-Sn-Pb type alloy which is formed into atomized alloy powder. The alloy power is processed through extrusion process. The proposed bearing metal has substantially high fatigue-resistance and high lubricating ability.
The proposed alloy is composed of Al as a matrix or principal component; one or more selected among Pb, Sn, In, Sb, Bi as lubricating component; Si as hardening component; one or more selected among Cu, Cr, Mg, Mn, Ni, Zn, Fe as reinforcement component. The lubricating component is added so that the area ratio versus Al matrix is in a range greater than 0.04 and smaller than or equal to 0.07. The hardening component is added so that the area ratio versus Al matrix is in a range of greater than or equal to 0.01 and smaller than or equal to 0.17. The reinforcement component is added in a content of 0.2 to 5.0 wt %. Further, if desired, one or more selected among Ti, B, Zr, V, Ga, one or more rare earth metal (REM) including Sc and Y can be added in a content of 0.01 to 3.0 Wt % to composite alloy. The lubricating component is prepared in a form of fine grain powder having grain side less than or equal to 8 .mu.m. The powder state lubricating component is uniformly dispersed in the powder state alloy. The powder state alloy is formed into a billet and processed through extrusion process in an extrusion ratio of greater than or equal to 10. The grain size of Si as hardening component is controlled to be smaller than or equal to 12 .mu.m, preferably in a range of 6 .mu.m to 12 .mu.m. The extrusion processed alloy has tensil stress greater than or equal to 12 Kgf/mm at normal temperature and has expansion under normal temperature is 11% in tensil test.
In such metal alloy, it is preferable to contain large content of Pb as lubricating component for better lubricating ability and higher heat-resistance, higher wear-resistance, higher corrosion-resistance, better oil affinity and so forth. However, when the content of Pb in the alloy exceeds 12 Wt %, Pb grain size becomes excessively large and Pb segregation is caused in the atomized powder processed from the metal at practically used temperature. Furthermore, due to gravitical segregation, fluctuation of Pb concentration can be caused. Excessive grain size of Pb tends to degrade fatigue-resistance of the alloy. Furthermore, due to fluctuation of content of Pb, local degradation of seizure resistance or fatigue-resistance is caused in the alloy. In such reason, the content of Pb is limited to be smaller than or equal to 12 Wt %.
In order to provide Pb content, attempt was made to prepare powder state Pb separately from Al alloy powder. The Pb powder is added to the Al alloy powder before extrusion. However, this attempt was not so successful because when Pb content is excess of 12 Wt % is added, liquid phase Pb molten by the heat in the extrusion process tends to bind Pb particles for forming excessively large size Pb grain in the alloy. Furthermore, presence of such liquid state Pb tends to cause extrusion defect in the extruded block.